How to implement many to many nova resource without building custom tool - laravel

Question

I am currently building a timetable generation system, I have these models below which are Subject and Teacher as the two main models with their nova resources, I have created a pivot model SubjectAllocation (has a nova resource) with a pivot table subject_allocations with fields teacher_id and subject_id. I would like to be able to use SubjectAllocation nova resource to select a teacher and allocate multiple subjects to this teacher but currently, I have no lack of it. Tried pulling in this package dillingham/nova-attach-many to attach to the SubjectAllocation model and this package to pick teachers records sloveniangooner/searchable-select but it cannot store data in the pivot table.
Subject Allocation Resource
<?php
namespace App\Nova;
use Illuminate\Http\Request;
use Laravel\Nova\Fields\BelongsToMany;
use Laravel\Nova\Fields\ID;
use Laravel\Nova\Http\Requests\NovaRequest;
use NovaAttachMany\AttachMany;
use Sloveniangooner\SearchableSelect\SearchableSelect;
class SubjectAllocation extends Resource
{
/**
* The model the resource corresponds to.
*
* #var string
*/
public static $model = 'App\SubjectAllocation';
/**
* The single value that should be used to represent the resource when being displayed.
*
* #var string
*/
public static $title = 'id';
/**
* The columns that should be searched.
*
* #var array
*/
public static $search = [
'id',
];
/**
* Get the fields displayed by the resource.
*
* #param \Illuminate\Http\Request $request
* #return array
*/
public function fields(Request $request)
{
return [
ID::make()->sortable(),
SearchableSelect::make('Teacher', 'teacher_id')->resource("teachers"),
AttachMany::make('Subjects')
->showCounts()
->help('<b>Tip: </b> Select subjects to be allocated to the teacher'),
];
}
/**
* Get the cards available for the request.
*
* #param \Illuminate\Http\Request $request
* #return array
*/
public function cards(Request $request)
{
return [];
}
/**
* Get the filters available for the resource.
*
* #param \Illuminate\Http\Request $request
* #return array
*/
public function filters(Request $request)
{
return [];
}
/**
* Get the lenses available for the resource.
*
* #param \Illuminate\Http\Request $request
* #return array
*/
public function lenses(Request $request)
{
return [];
}
/**
* Get the actions available for the resource.
*
* #param \Illuminate\Http\Request $request
* #return array
*/
public function actions(Request $request)
{
return [];
}
}
Fields Methods in Subject Resource
public function fields(Request $request)
{
return [
ID::make()->sortable(),
Text::make('Subject Name', 'name')
->withMeta(['extraAttributes' => ['placeholder' => 'Subject Name']])
->sortable()
->creationRules('required', 'max:255', 'unique:subjects,name')
->updateRules('required', 'max:255'),
Text::make('Subject Code', 'code')
->withMeta(['extraAttributes' => ['placeholder' => 'Subject Code']])
->sortable()
->creationRules('required', 'max:255', 'unique:subjects,code')
->updateRules('required', 'max:255')
,
Textarea::make('Description')
->nullable(),
BelongsToMany::make('Teachers'),
];
}
Fields method in Teacher Resource
public function fields(Request $request)
{
return [
ID::make()->sortable(),
BelongsTo::make('User')
->searchable(),
Text::make('First Name', 'first_name')
->withMeta(['extraAttributes' => ['placeholder' => 'First Name']])
->sortable()
->rules('required', 'max:50'),
Text::make('Middle Name', 'middle_name')
->withMeta(['extraAttributes' => ['placeholder' => 'Middle Name']])
->sortable()
->nullable()
->rules('max:50'),
Text::make('Last Name', 'last_name')
->withMeta(['extraAttributes' => ['placeholder' => 'Last Name']])
->sortable()
->rules('required', 'max:50'),
Text::make('Teacher Code', 'teacher_code')
->withMeta(['exraAttributes' => [ 'placeholder' => 'Teacher Code']])
->sortable()
->creationRules('required', 'max:50', 'unique:teachers,teacher_code')
->updateRules('required', 'max:50'),
BelongsToMany::make('Subjects'),
];
}
Any suggestion on how I can make it work or a better solution, would appreciate very much

Answer 1

Without build custom tool, use following method:
// app\Nova\SubjectAllocation.php
public function fields(Request $request)
{
return [
ID::make()->sortable(),
// SearchableSelect::make('Teacher', 'teacher_id')->resource("teachers"),
SearchableSelect::make('Teacher', 'teacher_id')->resource(\App\Nova\Teacher::class)
->displayUsingLabels(),
AttachMany::make('Subjects','subject_id')
->showCounts()
->help('<b>Tip: </b> Select subjects to be allocated to the teacher')
->fillUsing(function($request, $model, $attribute, $requestAttribute) {
$a = json_decode($request->subject_id, true);
$teacher = \App\Teacher::find($request->teacher_id);
if(count($a)==0){
// Error processing because no subject is choosen
}else if(count($a)==1){
$model['subject_id'] = $a[0];
}else{
$model['subject_id'] = $a[0];
array_shift ($a); // Remove $a[0] in $a
$teacher->subjects()->sync(
$a
);
}
})
];
}